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Date: Tue, 13 Dec 2022 23:42:36 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com>, ast@...nel.org, andrii@...nel.org, martin.lau@...ux.dev, john.fastabend@...il.com, song@...nel.org, yhs@...com, kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, bpf@...r.kernel.org, netdev@...r.kernel.org Cc: Sean Tranchetti <quic_stranche@...cinc.com> Subject: Re: [PATCH net] filter: Account for tail adjustment during pull operations On 12/13/22 5:39 AM, Subash Abhinov Kasiviswanathan wrote: > Extending the tail can have some unexpected side effects if a program is > reading the content beyond the head skb headlen and all the skbs in the > gso frag_list are linear with no head_frag - > > kernel BUG at net/core/skbuff.c:4219! > pc : skb_segment+0xcf4/0xd2c > lr : skb_segment+0x63c/0xd2c > Call trace: > skb_segment+0xcf4/0xd2c > __udp_gso_segment+0xa4/0x544 > udp4_ufo_fragment+0x184/0x1c0 > inet_gso_segment+0x16c/0x3a4 > skb_mac_gso_segment+0xd4/0x1b0 > __skb_gso_segment+0xcc/0x12c > udp_rcv_segment+0x54/0x16c > udp_queue_rcv_skb+0x78/0x144 > udp_unicast_rcv_skb+0x8c/0xa4 > __udp4_lib_rcv+0x490/0x68c > udp_rcv+0x20/0x30 > ip_protocol_deliver_rcu+0x1b0/0x33c > ip_local_deliver+0xd8/0x1f0 > ip_rcv+0x98/0x1a4 > deliver_ptype_list_skb+0x98/0x1ec > __netif_receive_skb_core+0x978/0xc60 > > Fix this by marking these skbs as GSO_DODGY so segmentation can handle > the tail updates accordingly. > > Fixes: 5293efe62df8 ("bpf: add bpf_skb_change_tail helper") > Signed-off-by: Sean Tranchetti <quic_stranche@...cinc.com> > Signed-off-by: Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com> > --- > net/core/filter.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index bb0136e..d5f7f79 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -1654,6 +1654,20 @@ static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp); > static inline int __bpf_try_make_writable(struct sk_buff *skb, > unsigned int write_len) > { > + struct sk_buff *list_skb = skb_shinfo(skb)->frag_list; > + > + if (skb_is_gso(skb) && list_skb && !list_skb->head_frag && > + skb_headlen(list_skb)) { > + int headlen = skb_headlen(skb); > + int err = skb_ensure_writable(skb, write_len); > + > + /* pskb_pull_tail() has occurred */ > + if (!err && headlen != skb_headlen(skb)) > + skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY; > + > + return err; > + } __bpf_try_make_writable() does not look like the right location to me given this is called also from various other places. bpf_skb_change_tail has skb_gso_reset in there, potentially that or pskb_pull_tail itself should mark it? > return skb_ensure_writable(skb, write_len); > } > >
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